9.22 ATAN2 — Arctangent function

Description:

ATAN2(Y, X) computes the principal value of the argument function of the complex number X + i Y. This function can be used to transform from Cartesian into polar coordinates and allows to determine the angle in the correct quadrant.

Standard:

Fortran 77 and later

Class:

Elemental function

Syntax:

RESULT = ATAN2(Y, X)

Arguments:

Y	The type shall be REAL.
X	The type and kind type parameter shall be the same as Y. If Y is zero, then X must be nonzero.

Return value:

The return value has the same type and kind type parameter as Y. It is the principal value of the complex number X + i Y. If X is nonzero, then it lies in the range -\pi \le \atan (x) \leq \pi. The sign is positive if Y is positive. If Y is zero, then the return value is zero if X is strictly positive, \pi if X is negative and Y is positive zero (or the processor does not handle signed zeros), and -\pi if X is negative and Y is negative zero. Finally, if X is zero, then the magnitude of the result is \pi/2.

Example:

          program test_atan2
            real(4) :: x = 1.e0_4, y = 0.5e0_4
            x = atan2(y,x)
          end program test_atan2

Specific names:

Name	Argument	Return type	Standard
ATAN2(X, Y)	REAL(4) X, Y	REAL(4)	Fortran 77 and later
DATAN2(X, Y)	REAL(8) X, Y	REAL(8)	Fortran 77 and later